It is known, that joint hyaline cartilage degradation or damage due to trauma, intervertebral disc traumatic disease, or intervertebral chronic and progressive degeneration finally lead to local contact between bony surfaces. As these surfaces are in constant motion relative to each other, this contact leads to severe pain for the patient as well as to a further and accelerated destruction of the remaining compliant tissue.
Therefore restoring the gap between bones having an undesired contact will reduce pain, diminish or even anneal further destruction and may restore a balance closer to a healthy articulation. Several methods, aiming at the amelioration of the load bearing and/or articulation and at the prevention of further destruction of the compliant tissue, have been developed in the last decades.
Implants from cell culture allow the reparation of the tissue and reduce pain, but in general are very expensive, do not act as a gap filler and are not long lasting.
Articular cartilage and meniscal cartilage provide the mobile weight bearing surfaces of the knee joint. Damage to these surfaces is generally due to genetic predisposition, disease, trauma, and/or aging. The result is usually the development of chondromalacia, thinning and softening of the articular cartilage, and degenerative tearing of the cartilage. Most commonly, the cartilage is damaged by osteoarthritis. Articular cartilage has only limited ability to heal due to lack of a direct blood supply. Because the cartilage layer lacks nerve fibres, patients are often unaware of the severity of the damage. During the final stage of osteoarthritis, an affected joint consists of bone articulating against bone, which leads to severe pain and reduced mobility. By the time patients seek medical treatment, surgical intervention may be required to alleviate pain and repair the cartilage damage.
Various methods of treatment are available. Each option usually has specific indications and is accompanied by a list of benefits and deficiencies that may be compared to other options. Nonsteroidal anti-inflammatory drugs (NSAIDS), cortisone injections, hyaluronic acid injections, arthroscopic debridement, osteotomy, uni-compartmental knee replacement, and total knee replacement are used depending on the severity of the damage.
Currently, there is a void in options used to treat the relatively young patient with moderate to severe diseased or defective cartilaginous tissue involving mainly one compartment of the knee. Some patients cannot tolerate or do not want the risk of potential side effects of NSAIDS. Repeated cortisone injections actually weaken articular cartilage after a long period of time and do not protect the cartilage. Arthroscopic debridement alone frequently does not provide long lasting relief of symptoms. Uni-compartmental and bi-compartmental total knee replacements resect significant amounts of bone and may require revision surgery when mechanical failure occurs. Therefore, it is best to delay this type of bone resecting surgery as long as possible.
One approach has been to implant a compliant device in the inter-condylar void space. In theory, such devices cushion the femoral and tibial bearings surfaces and distribute loads uniformly over a larger portion of the knee joint due to the ability of these devices to elastically deform and ensure the gap between both bearing surfaces. This ability to deform can also be a detriment, with regard to the poor fatigue behaviour of such device undergoing too large deformation resulting into tearing or disintegration.
U.S. Pat. No. 6,206,927 discloses a self-centering meniscal prosthesis device suitable for minimally invasive, surgical implantation into the cavity between a femoral condyle and the corresponding tibial plateau. The prosthesis is composed of a hard, high modulus material shaped such that the contour of the device and the natural articulation of the knee exerts a restoring force on the free-floating device.
US-A-2005/278025 discloses a prosthesis for placement into a joint space between two or more bones. The prosthesis includes a body formed from a pre-formed solid one piece elastomer, wherein the elastomer is formed from a synthetic organic polymer that is biocompatible and has a uniform modulus of elasticity and a mechanical strength between 0.5 MPa and 75 MPa. Preferably, the body has a shape contoured to fit within a joint space between the femoral condyle, tubercle, and tibial plateau without any means of attachment. The prosthesis is uni-compartmental, i.e. is adapted for implantation into a compartment defined by the space between the tibial plateau and a femoral condyle. Thus, the prosthesis is suited for use in either a lateral compartment or a medial compartment. Where it is necessary to replace menisci in both compartments, two prostheses are required.
The intervertebral disc functions to stabilize the spine and to distribute forces between vertebral bodies. The intervertebral disc is composed primarily of three structures: the nucleus pulposus, the annulus fibrosis, and two vertebral end-plates. These components work together to absorb the shock, stress, and motion imparted to the human vertebrae. Intervertebral discs may be displaced or damaged due to trauma or disease. One way to relieve the symptoms of these conditions is by surgical removal of a portion or all of the intervertebral disc or by implanting an artificial device to replace the damaged portion of the patient's intervertebral disc.
WO-A-2004/108022 discloses an intervertebral disc implant that comprises an elastomeric polymer body, in particular a hydrogel body, and a super elastic element. The implant for the spinal disc space, in a preferred embodiment comprises an elongated hydrogel body and an elongated core element comprised of a super elastic nickel-titanium alloy.
US-A-2006/0241759 discloses a polymeric spinal implant wherein the polymer material is substantially uniformly oriented to create anisotropic properties, especially increased strength perpendicular to the orientation of the polymer material. In moulded polymeric materials, increased anisotropic rigidity or strength may be achieved by substantially orienting the polymer chains in the material during processing, for example by slowly cooling from melt state or by application of pressure (e.g. in an injection molding process).
WO-A-2007/139949 discloses a spinal intervertebral disc implant comprising a solid elastomeric body with mechanical compressive and/or tensile elasticity of from 1 MPa to 100 MPa. The implant can be configured with a single, uniform average durometer material and/or may have non-linear elasticity. The implant can be configured to be stiffer in the middle, or stiffer on the outside perimeter. The implant can further be configured to have a continuous stiffness change.
EP-A-0919209 discloses a prosthetic nucleus for a vertebral disc made of a hydrogel material and exhibiting diminished lateral bulging under high compressive loads, wherein the anterior periphery preferably has a stiffness of from 0.1 to 1.5 MPa, and the posterior periphery has a stiffness at least 10% less than that of the anterior periphery, wherein the increase in stiffness from the anterior to the posterior sides can be either gradual or sudden.
WO-A-2008/064119 discloses a multi-component implantable spinal disk comprising an external shell, a first endplate, a second endplate, plural attachment devices and a core internal component, wherein the external shell preferably has a Young modulus of elasticity of from 7 to 13 MPa and the core internal component has a Young modulus of elasticity of from 3 to 8 MPa, wherein the core internal component may comprise vertical reinforcement columns with a Young modulus of elasticity of from 6 to 13 MPa.
WO-A-2005/077304 generally discloses a multi-component load bearing biocompatible device, in particular an implantable spinal disc prosthesis, which may comprise multiple regions of varying elasticity. For example the upper portion and lower portion can be less elastic and more rigid than the inner region. The implantable spinal disc prosthesis further may have an intermediate region of elasticity.
EP-A-0642775 discloses a multi-component implantable spinal disc comprising a first and second endplate, wherein up to three layers of different polymers, preferably with different compressibility for each polymer, are arranged in between the two endplates to form the multi-component implantable spinal disc.
However, none of the prior art so far has been able to achieve a compliant material or device capable of providing structural and tribological properties similar to native tissue.
Surprisingly it has now been found that an implant device of the present invention solves the problems described above.